1. Field of the Invention
The present invention relates to an optical receiver module providing a semiconductor optical amplifier (SOA), in particular, the invention relates to an optical receiver module that suppresses stray light caused by an amplified spontaneous emission (ASE) of the SOA from affecting a semiconductor photodiode (PD) that receives an optical signal amplified by the SOA.
2. Related Background Arts
Recent optical communication system often provides an SOA to amplify attenuated optical signal. FIG. 10 schematically illustrates a functional block diagram of a conventional optical receiver module, which includes an SOA 100, a semiconductor optical device 102 that receives an optical signal amplified by the SOA 100. The SOA 100 and the optical device 102 are commonly enclosed within a housing 104, and the housing 104 provides a coupling unit 106 to couple an external optical fiber therewith. The optical signal is provided from the external optical fiber to the SOA through the coupling unit 106.
The SOA often accompanies with an amplified spontaneous emission (ASE) which may be a source of stray light. The optical device 102, not only the amplifier optical signal coming from the SOA 100, but receives the stray light as noise light, which degrades the optical sensitivity of the receiver module. When the optical device is a light emitting device, typically, a semiconductor laser diode, the stray light entering the optical device 102 degrades the performance, namely, the coherency of the laser diode.